1. Field of the Invention
The present invention relates to compositions and methods for acidizing wells such as oil and gas wells in which corrosion inhibitors are employed to lessen the corrosive effects of hydrochloric acid on metal surfaces.
2. Description of the Prior Art
Hydrochloric acid solutions are commonly utilized in treatments carried out to stimulate oil and gas wells. In a general acidizing treatment, an aqueous hydrochloric acid solution is introduced into a subterranean formation to react with acid soluble materials in the formation and enlarge pore spaces in the formation. In a fracture acidizing treatment, a fracture is produced in a subterranean formation and an aqueous hydrochloric acid solution is introduced into the fracture to etch flow channels in the face thereof. The hydrochloric acid solution also enlarges pore spaces in the fracture face and in the formation. Hydrochloric acid solutions are also utilized to merely clean out well bores in order to facilitate the flow of hydrocarbons therethrough.
A problem associated with the treatment of an oil and gas well with a hydrochloric acid solution is corrosion by the solution of metal surfaces of casing, tubing and other equipment in the well bore as well as equipment such as mixing tanks and pumps used in association with the treatment. If corrosion by the solution is not inhibited, the surfaces can be seriously damaged. The expense of repairing or replacing damaged equipment is extremely high. Also, the corrosive action of the solution can substantially neutralize the solution before it enters the formation and result in the undesirable introduction of metal ions into the formation. Corrosion by the solution is exacerbated by high temperature and pressure conditions.
Various hydrochloric acid acidizing compositions that include corrosion inhibitors for diminishing the corrosive effects of the acid on metal-surfaces have been developed and used heretofore. The types of components employed in the corrosion inhibitors vary depending upon the nature of the compositions, the types of metal surfaces involved, associated environmental conditions and so forth.
Equipment formed of titanium based alloys is sometimes used in conjunction with equipment formed of ferrous based alloys such as low alloy steel. For example, in oil and gas wells, titanium based alloys are often used in association with wellhead equipment and down hole tooIs and tubular goods (e.g., air lift lines) to provide extra strength and corrosion resistance thereto. Due to economic and other reasons, most of the remaining tubular goods and equipment are formed of ferrous based alloys such as low alloy steel.
The use of equipment formed of titanium based alloys together with equipment formed of ferrous based alloys such as low alloy steel presents special problems with respect to inhibiting the corrosive effects of aqueous hydrochloric acid solutions on the surfaces of the equipment. Chemical reducing compounds such as unsaturated carbonyl compounds and unsaturated alcohols, e.g., acetylenic alcohols, are typically used as corrosion inhibitors for ferrous based alloys such as low alloy steel. On the other hand, in order to effectively inhibit corrosion of titanium based alloys in an environment associated with hydrochloric acid, a strong oxidizing agent is required. Unfortunately, reducing compounds for ferrous based alloys are not normally compatible with strong oxidizing agents. For example, although sodium nitrate, a potent oxidizing agent, will sufficiently protect titanium based alloys from corrosion by hydrochloric acid, it will substantially interfere with the reduction characteristics of the reducing compounds and prevent the reducing compounds from protecting the ferrous based alloys. Interaction of the sodium nitrate with the reducing compounds will also diminish the ability of the sodium nitrate to protect the titanium based alloys.
There is a need for a hydrochloric acid acidizing composition that includes a corrosion inhibitor that protects both titanium based alloy surfaces and ferrous based alloy surfaces from the corrosive effects of the acid.